CARBONIC ACID AND VENTILATION. 107 



every beat less^ the corresponding amount is taken from 

 the circulation. But even this is not the whole difference 

 because the beats become excessively feeble. The blood 

 seemed to require to remain in the lungs rather longer^ in 

 order to obtain its oxygen, whilst the breathing supplied 

 air more rapidly ; so that in some cases there were found 

 to be an addition of nearly one-half the number of inspira- 

 tions. In one case especially the pulse was raised, not 

 sunk ', and in most cases it was raised a little for a short 

 time at first, as if an inferior blood were endeavouring to 

 do equal work by moving more rapidly. 



Medical men have objected to the argument that any 

 evil result can arise from these effects, saying that man is 

 formed so as to resist such influences, and is not so weak 

 as to be confined within such small limits. When the 

 ground gives way under a man he cannot resist, he can 

 generate no force contrary to gravitation, except a few 

 movements or leaps from the ground itself if the sinking 

 is not too rapid. When the heart ceases beating man 

 cannot resist, as he needs the beating heart itself to gene- 

 rate his power. If the heart is feeble, he may breathe fast to 

 supply it rapidly with oxidized blood, and to a certain ex- 

 tent succeeds ; but he must take this compensation force 

 from some place. I cannot pretend to give an opinion on 

 the result of an unnatural slowness of pulse, and an un- 

 natural rapidity of breathing ; but that they are evil omens 

 is true, or we have long been deceived. In mines and 

 such places the evil is exaggerated, because the exertion 

 required to climb the ladders leads to an increased activity 

 of the heart. 



If the gas by which the oxygen in air is diluted were 

 insoluble, the result might be very different, and we might 

 probably remain in air with less than lo per cent, of 

 oxygen. In one condition, namely, in high regions, some- 

 thing similar to this occurs; the amount of oxygen is 



